1. Field of the Invention
This invention relates to an engine, and more particularly, a small four-cycle utility engine which is particularly suitable for typical power tools driven by a vertical or horizontal power shaft.
2. Description of the Related Art
U.S. Pat. No. 7,287,508 to Kurihara and U.S. Pat. No. 7,624,714 to Kurihara et al. disclose a prior art small four-cycle engine construction for portable power tools.
Portable power tools such as line trimmers, blowers/vacuums, and chain saws must be able to run in a very wide range of orientations. However, in most power tools such as generators or tillers/cultivators, power shaft orientation is either substantially horizontal or vertical. Therefore, it is not necessary for these typical power tools to be able to run in a very wide range of orientations having complicated and economically ineffective constructions as in the above-referenced inventions.
For some tillers/cultivators powered by four-cycle engines with a vertical power shaft, lubrication also becomes a serious problem since it is difficult to use the same lubrication system as engines with a horizontal power shaft.
U.S. Pat. No. 6,250,273 to Ryuu et al. discloses a utility engine for horizontal and vertical shaft orientations. However, constructions are still complicated because special rotating parts having shafts other than a crankshaft or a camshaft are necessary for lubrication and speed control.
Therefore, it is an object of the present invention to provide a small four-cycle utility engine having an internal lubrication system, which is especially suitable for both vertical and horizontal power shaft engines.
It is a further object of the present invention to provide a small four-cycle utility engine having a speed control system enabling the engine to be run at a desired speed at any load, which is especially suitable for both vertical and horizontal power shaft engines.
It is yet a further object of the invention to provide a breathing system to work effectively throughout the normal range of operating positions, which is especially suitable for both vertical and horizontal power shaft engines.
It is yet a further object of the invention to provide a commonality of main parts between vertical and horizontal engines, which is especially suitable for both vertical and horizontal power shaft engines to reduce manufacturing cost.
These and other objects, features, and advantages of the present invention will become apparent upon further review of the remainder of the specification and the accompanying drawings.